U.S. patent application number 13/599169 was filed with the patent office on 2013-03-07 for magnetoresistance device.
This patent application is currently assigned to Agency fo Science, Technology and Research. The applicant listed for this patent is Seidikkurippu Nellainayagam Piramanayagam, Rachid Sbiaa, Taiebeh Tahmasebi. Invention is credited to Seidikkurippu Nellainayagam Piramanayagam, Rachid Sbiaa, Taiebeh Tahmasebi.
Application Number | 20130059168 13/599169 |
Document ID | / |
Family ID | 47753398 |
Filed Date | 2013-03-07 |
United States Patent
Application |
20130059168 |
Kind Code |
A1 |
Tahmasebi; Taiebeh ; et
al. |
March 7, 2013 |
Magnetoresistance Device
Abstract
A magnetoresistance device is provided. The magnetoresistance
device includes a hard magnetic layer, and a soft magnetic layer
having a multi-layer stack structure. The multi-layer stack
structure has a first layer of a first material and a second layer
of a second material. The first material includes cobalt iron boron
and the second material includes palladium or platinum.
Inventors: |
Tahmasebi; Taiebeh;
(Singapore, SG) ; Piramanayagam; Seidikkurippu
Nellainayagam; (Singapore, SG) ; Sbiaa; Rachid;
(Singapore, SG) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Tahmasebi; Taiebeh
Piramanayagam; Seidikkurippu Nellainayagam
Sbiaa; Rachid |
Singapore
Singapore
Singapore |
|
SG
SG
SG |
|
|
Assignee: |
Agency fo Science, Technology and
Research
|
Family ID: |
47753398 |
Appl. No.: |
13/599169 |
Filed: |
August 30, 2012 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61529269 |
Aug 31, 2011 |
|
|
|
Current U.S.
Class: |
428/811.2 |
Current CPC
Class: |
H01L 43/10 20130101;
H01L 43/08 20130101; G11C 11/161 20130101; Y10T 428/1121 20150115;
H01F 10/3236 20130101; G11C 11/16 20130101; H01F 10/3272 20130101;
H01F 10/123 20130101; H01F 10/3295 20130101; H01F 10/3286
20130101 |
Class at
Publication: |
428/811.2 |
International
Class: |
G11C 7/00 20060101
G11C007/00 |
Claims
1. A magnetoresistance device, comprising: a hard magnetic layer; a
soft magnetic layer comprising a multi-layer stack structure;
wherein the multi-layer stack structure has a first layer of a
first material and a second layer of a second material; wherein the
first material comprises cobalt iron boron and the second material
comprises palladium or platinum.
2. The magnetoresistance device of claim 1, wherein the multi-layer
stack structure comprises one or more stacks; wherein each stack
has a first layer of the first material and a second layer of the
second material.
3. The magnetoresistance device of claim 2, wherein the number of
stacks of the multi-layer stack structure ranges from 2 to 20.
4. The magnetoresistance device of claim 1, wherein the hard
magnetic layer comprises any one of a group consisting of cobalt
platinum, iron platinum, and a multi-layer stack structure having a
first layer of cobalt and a second layer of material comprising a
material or a combination of materials selected from a group of
materials consisting of platinum, palladium, iron palladium and
nickel.
5. The magnetoresistance device of claim 1, further comprising a
spacer layer disposed between the hard magnetic layer and the soft
magnetic layer.
6. The magnetoresistance device of claim 5, wherein the spacer
layer comprises any one of a group consisting of magnesium oxide,
stack of magnesium and magnesium oxide, copper and aluminum oxide
(Al.sub.xO.sub.y).
7. The magnetoresistance device of claim 5, further comprising: a
first spin-polarizing layer structure disposed between the spacer
layer and the soft magnetic layer; and a second spin-polarizing
layer structure disposed between the spacer layer and the hard
magnetic layer.
8. The magnetoresistance device of claim 7, wherein the first
spin-polarizing layer structure comprises one or more layers, each
layer having a different thickness; wherein each layer of the first
spin-polarizing layer structure comprises any one of a group
consisting of cobalt iron boron, iron, cobalt and cobalt iron;
wherein the second spin-polarizing layer structure comprises one or
more layers, each layer having a different thickness; wherein each
layer of the second spin-polarizing layer structure comprises any
one of a group consisting of cobalt iron boron, cobalt, iron and
cobalt iron.
9. The magnetoresistance device of claim 7, further comprising a
seed layer structure; wherein the soft magnetic layer is disposed
between the seed layer structure and the first spin-polarizing
layer structure.
10. The magnetoresistance device of claim 9, wherein the seed layer
structure comprises at least one layer; wherein the at least one
layer of the seed layer structure comprises a material or a
combination of materials selected from a group of materials
consisting of tantalum, chromium, titanium, nickel, tungsten,
ruthenium, palladium, platinum, zirconium, hafnium, silver, gold,
aluminum, antimony, molybdenum, tellurium, cobalt iron, cobalt iron
boron and cobalt chromium.
11. The magnetoresistance device of claim 10, wherein the at least
one layer of the seed layer structure is a conductive
electrode.
12. The magnetoresistance device of statement 11, wherein the at
least one layer of the seed layer structure, when used as the
electrode, has a thickness greater than 7 nm.
13. The magnetoresistance device of claim 11, further comprising a
capping layer structure; wherein the hard magnetic layer is
disposed between the capping layer structure and the second
spin-polarizing layer structure.
14. The magnetoresistance device of claim 13, wherein the capping
layer structure is part of the electrode.
15. The magnetoresistance device of claim 14, wherein the capping
layer structure comprises at least one layer, wherein the at least
one layer of the capping layer structure comprises a material or a
combination of materials selected from a group of materials
consisting of tantalum, chromium, titanium, nickel, tungsten,
ruthenium, palladium, platinum, zirconium, hafnium, silver, gold,
aluminum, antimony, molybdenum, tellurium and cobalt chromium.
16. The magnetoresistance device of claim 1, wherein the soft
magnetic layer further comprises a further multi-layer structure;
wherein the multi-layer structure and the further multi-layer
structure are coupled antiferromagnetically to each other.
17. The magnetoresistance device of claim 16, wherein the
antiferromagnetic coupling between the multi-layer structure and
the further multi-layer structure are obtained through the use of
thin layers of one or more materials selected from a group
consisting of ruthenium, rhodium, and an alloy of ruthenium and
rhodium.
18. A magnetoresistance device, comprising: a hard magnetic layer;
a soft magnetic layer comprising a multi-layer stack structure;
wherein the multi-layer stack structure has a first layer of a
first material and a second layer of a second material; wherein the
first material comprises a cobalt based magnetic material.
19. The magnetoresistance device of claim 18, wherein the cobalt
based magnetic material has a formula Co--X--Y; wherein X comprises
iron and Y comprises boron or boron nitride.
20. The magnetoresistance device of claim 18, wherein the second
material comprises any one of a group consisting of platinum,
palladium and nickel.
Description
[0001] This application claims the benefit of U.S. Provisional
Application No. 61/529,269, filed Aug. 31, 2011.
FIELD OF THE INVENTIONS
[0002] Various embodiments relate generally to a magnetoresistance
device.
BACKGROUND OF THE INVENTIONS
[0003] Magnetic random access memory (MRAM) is emerging as an
alternative to conventional semiconductor memories. Compared to
static random access memory (SRAM) and dynamic random access memory
(DRAM), the MRAM has an advantage of non-volatility. Compared to
flash memory used for storage of information, the MRAM has an
advantage of endurance. MRAM devices may have advantages of
non-volatility, practically infinite write endurance, and short
read and write times. In order to compete with flash memory, it is
desirable to increase the density of the MRAM cells in a chip,
which may involve keeping the MRAM cells as small as possible. In
order to compete with SRAM and DRAM, it is desirable to increase
the speed of operation without compromising the density. Further,
it is also desirable to achieve low current switching without
compromising thermal stability.
[0004] Memory elements for MRAMs may include giant magnetoresistive
(GMR) spin valves (SV). The GMR-SV may include two ferromagnetic
layer separated by a non-magnetic metallic spacer layer. However, a
larger magnetoresistance (MR) signal has been found in Magnetic
Tunnel Junction (MTJ) devices where the tunneling magnetoresistance
(TMR) occurs due to the use of an insulator layer between the
ferromagnetic layers instead of a metallic spacer layer. The MTJ
devices can be used in MRAM devices, where the difference in the
resistance between two remanent states can be used to represent
digital bits 0 and 1.
[0005] Spin-torque transfer based MRAMs (STT-MRAMs) can be scalable
to very small sizes (e.g. 5 nm of FePt material, based on the
thermal stability considerations only) as compared to
field-switchable MRAM devices. However, the smallest possible cell
size is not only limited by thermal stability, but also by the
writability. Devices with FePt may require a large write current
required for the write operation. Moreover, two geometries, one
with magnetization in plane and another with magnetization
out-of-plane (perpendicular), are being investigated.
[0006] Magnetic layers with in-plane and perpendicular anisotropy
can be used in memory element structures. Magnetic layers with
perpendicular magnetic anisotropy (PMA) may have several advantages
over conventional in-plane magnetized layers such as improved
thermal stability, scalability and low spin transfer torque (STT)
switching current for nanoscale Spin Transfer Torque MRAM
(STT-MRAM). Therefore, magnetic layers with PMA may be used for
realizing a practical and scalable STT-MRAM.
[0007] Materials with high PMA such as cobalt (Co)/palladium (Pd)
or cobalt (Co)/platinum (Pt) magnetic multilayers and also iron
palladium (FePt) or cobalt platinum (CoPt) alloys can be considered
for forming magnetic layers with PMA. The alloy films with PMA such
as L1.sub.0-FePt, L1.sub.0-CoPt and ordered Co.sub.3Pt may exhibit
extremely large magnetocrystalline anisotropy (up to
7.times.10.sup.7 erg/cm.sup.3 for FePt) due to the spin-orbit
coupling of platinum, and the strong hybridization between the Pt
5d and Co or Fe 3d electronic states. The easy axis of chemically
ordered L1.sub.0-FePt and L1.sub.0-CoPt ferromagnetic materials
which lies along (001) crystal orientation can be used in MTJ
devices to achieve a better thermal stability due to the larger
anisotropy constant, and therefore, may allow potential scaling of
the MTJ devices down to 5 nm.
[0008] The Co/Pd, Co/Pt, Co/nickel (Ni), etc magnetic multilayers
have been widely investigated due to their wide applications and
relative ease in achieving perpendicular magnetic anisotropy (PMA).
Although Co/Pd, Co/Pt magnetic multilayers and FePt alloy possess
desired properties for the hard layers of the MRAM devices (that
retain their magnetization direction), their use as the soft layer
is difficult. Devices based on Co/Pd multilayers or FePt layers
have a high anisotropy constant and hence they can retain their
magnetization in a stable manner. However, as the writing current
is also proportional to the anisotropy constant, such materials
need a high current to switch, posing a limitation in the
transistor size (or the density of cells) or in the operating
speed.
SUMMARY
[0009] According to one embodiment, a magnetoresistance device is
provided. The magnetoresistance device includes a hard magnetic
layer, and a soft magnetic layer having a multi-layer stack
structure. The multi-layer stack structure has a first layer of a
first material and a second layer of a second material. The first
material includes cobalt iron boron and the second material
includes palladium or platinum.
[0010] According to another embodiment, a magnetoresistance device
is provided. The magnetoresistance device includes a hard magnetic
layer, and a soft magnetic layer having a multi-layer stack
structure. The multi-layer stack structure has a first layer of a
first material and a second layer of a second material. The first
material includes a cobalt based magnetic material.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] In the drawings, like reference characters generally refer
to the same parts throughout the different views. The drawings are
not necessarily to scale, emphasis instead generally being placed
upon illustrating the principles of the invention. In the following
description, various embodiments of the invention are described
with reference to the following drawings, in which:
[0012] FIG. 1 shows a three-dimensional view of a magnetoresistance
device according to one embodiment.
[0013] FIG. 2 shows a schematic diagram of a multi-layer stack
structure of a soft magnetic layer of a magnetoresistance device
according to one embodiment.
[0014] FIG. 3 shows a three-dimensional view of a magnetoresistance
device according to one embodiment.
[0015] FIG. 4 shows a schematic diagram of a magnetoresistance
device according to one embodiment.
[0016] FIG. 5 shows a graph illustrating a hysteresis loop of a
magnetoresistance device for different thicknesses of a seed layer
structure according to one embodiment.
[0017] FIG. 6 shows a graph illustrating a magnetoresistance
behavior of a magnetoresistance device for different thicknesses of
a seed layer structure according to one embodiment.
[0018] FIG. 7 shows a graph illustrating a magnetoresistance
behavior of a magnetoresistance device according to one
embodiment
[0019] FIG. 8 shows a graph illustrating switching behavior of a
conventional device.
[0020] FIG. 9 shows a switching field of a soft magnetic layer of a
magnetoresistance device and magnetoresistance of the
magnetoresistance device plotted against a size of the
magnetoresistance device according to one embodiment.
DETAILED DESCRIPTION OF THE INVENTIONS
[0021] Embodiments of a magnetoresistance device will be described
in detail below with reference to the accompanying figures. It will
be appreciated that the embodiments described below can be modified
in various aspects without changing the essence of the
invention.
[0022] In one embodiment, the magnetoresistance device may include
a hard magnetic layer and a soft magnetic layer having a
multi-layer stack structure. The multi-layer stack structure may
have a first layer of a first material and a second layer of a
second material. The first material may include cobalt iron boron
and the second material may include palladium or platinum.
[0023] In another embodiment, the magnetoresistance device may
include a hard magnetic layer, and a soft magnetic layer having a
multi-layer stack structure. The multi-layer stack structure may
have a first layer of a first material and a second layer of a
second material. The first material may include a cobalt based
magnetic material. The cobalt based magnetic material may have a
formula Co--X--Y. In one embodiment, X may include iron, and Y may
include boron or boron nitride. The second material may include
platinum, palladium or nickel.
[0024] FIG. 1 shows a three-dimensional view of a magnetoresistance
device 100 according to one embodiment. The magnetoresistance
device 100 has a hard magnetic layer 102 and a soft magnetic layer
104. In one embodiment, the soft magnetic layer 104 has a
multi-layer stack structure 200 as shown in FIG. 2. The multi-layer
stack structure 200 has one or more stacks 202. The number of
stacks 202 of the multi-layer stack structure 200 ranges from 2 to
20. The number of stacks 202 may affect the stability of the soft
magnetic layer 104. When the number of stacks 202 is larger, the
soft magnetic layer 104 is thicker and is more stable.
[0025] Each stack 202 has a first layer 204 of the first material
and a second layer 206 of the second material. In one embodiment,
the first material may include cobalt iron boron (CoFeB) and the
second material may include palladium (Pd) or platinum (Pt). The
multi-layer stack structure 200 may have an alternating arrangement
of the first layer 204 of the first material and the second layer
206 of the second material. The soft magnetic layer 104 has a
CoFeB/Pd or CoFeB/Pt multi-layer structure.
[0026] Cobalt iron boron, palladium and platinum have high
anisotropy. Thus, using cobalt iron boron and palladium or platinum
in the soft magnetic layer 104 can make the perpendicular magnetic
anisotropy (PMA) in the soft magnetic layer 104 to be stronger.
Therefore, the soft magnetic layer 104 may be more stable. As such,
it may be possible to reduce the size of the magnetoresistance
device 100 to e.g. below 40 nm. The magnetoresistance device 100
having a reduced size may be used for higher storage density.
[0027] A value of magnetization for the first layer 204 of the
first material (e.g. the first layer 204 of cobalt iron boron) may
be chosen to reduce a switching current and to improve the
perpendicular magnetic anisotropy (PMA). The perpendicular magnetic
anisotropy (PMA) of the soft magnetic layer 104 may be controlled
for suitable thermal stability by using the thickness of the second
layer 206 of the second material or by using seed layers.
[0028] The first layer 204 of cobalt iron boron may have optimized
concentration of cobalt and iron. In one embodiment, the CoFeB
composition may be Co.sub.20Fe.sub.60B.sub.20. The switching
current can be optimized by varying the composition of CoFeB.
[0029] In one embodiment, the first layer 204 of the first material
and the second layer 206 of the second material may have the same
thickness. In another embodiment, the first layer 204 of the first
material and the second layer 206 of the second material may have
different thicknesses. The first layer 204 of the first material
may have a thickness ranging from about 0.25 nm to about 0.6 nm.
The second layer 206 of the second material may have a thickness
ranging from about 0.4 nm to about 1.2 nm.
[0030] Referring back to FIG. 1, the hard magnetic layer 102 may
include any hard layer with perpendicular magnetic anisotropy
(PMA). The hard magnetic layer 102 may include but is not limited
to cobalt platinum (e.g. L1.sub.0 CoPt) and iron platinum (e.g.
L1.sub.0 FePt). The hard magnetic layer 102 may also include a
multi-layer stack structure. The multi-layer stack structure of the
hard magnetic layer 102 may be similar to the multi-layer stack
structure 200 of the soft magnetic layer 104. The multi-layer stack
structure of the hard magnetic layer 102 may have a first layer of
cobalt and a second layer of material. The first layer of cobalt
and a second layer of material may be arranged in an alternating
arrangement. The material used for the second layer may include but
is not limited to platinum, palladium, iron palladium and nickel.
The material used for the second layer may also include a
combination of materials including but not limited to platinum,
palladium, iron palladium and nickel.
[0031] In one embodiment, the multi-layer stack structure of the
hard magnetic layer 102 may have ten stacks. Each stack may have a
first layer of palladium and a second layer of cobalt. Each first
layer of palladium may have a thickness ranging between about 5
.ANG. to about 15 .ANG.. Each second layer of cobalt may have a
thickness ranging between about 5 .ANG. to about 20 .ANG..
[0032] The magnetoresistance device 100 may also include a spacer
layer 106 disposed between the hard magnetic layer 102 and the soft
magnetic layer 104. In one embodiment, the spacer layer 106 may
include copper. In another embodiment, the spacer layer 106 may
include magnesium oxide (MgO), aluminum oxide (AlO) or alumina
(Al.sub.2O.sub.3) for achieving higher tunneling magnetoresistance
(TMR). In another embodiment, the spacer layer 106 may include
stack of magnesium or magnesium oxide or aluminum oxide
(Al.sub.xO.sub.y). The spacer layer 106 may have a thickness
ranging between about 8 .ANG. to about 20 .ANG..
[0033] The magnetoresistance device 100 may further include a first
spin-polarizing layer structure 108 and a second spin-polarizing
layer structure 110. The first spin-polarizing layer structure 108
is disposed between the spacer layer 106 and the soft magnetic
layer 104. The second spin-polarizing layer structure 110 is
disposed between the spacer layer 106 and the hard magnetic layer
102.
[0034] The first spin-polarizing layer structure 108 has one or
more layers. The one or more layers of the first spin-polarizing
layer structure 108 may be arranged in a stack. Each layer of the
first spin-polarizing layer structure 108 may include but is not
limited to cobalt iron boron (CoFeB), cobalt, iron and cobalt iron.
Each layer of the first spin-polarizing layer structure 108 may
have a different thickness. The first spin-polarizing layer
structure 108 may have a thickness ranging from about 0.2 nm to
about 3 nm.
[0035] The second spin-polarizing layer structure 110 has one or
more layers. The one or more layers of the second spin-polarizing
layer structure 110 may be arranged in a stack. Each layer of the
second spin-polarizing layer structure 110 may include but is not
limited to cobalt iron boron (CoFeB), cobalt, iron and cobalt iron.
Each layer of second spin-polarizing layer structure 110 may have a
different thickness. The second spin-polarizing layer structure 110
may have a thickness ranging from about 0.2 nm to about 3 nm.
[0036] The first spin-polarizing layer structure 108 and the second
spin-polarizing layer structure 110 may be disposed adjacent to the
spacer layer 106 in order to achieve higher magnetoresistance (MR).
The thicknesses of the first spin-polarizing layer structure 108
and the second spin-polarizing layer structure 110 may be varied
between about 0.2 nm and about 3 nm to increase the
magnetoresistance value. A larger thickness for the first
spin-polarizing layer structure 108 and the second spin-polarizing
layer structure 110 is desirable to prevent the transfer of fcc
(111) texture from the soft magnetic layer 104 to the spacer layer
106 or from the seed layer (details of which will be described
later) to the spacer layer 106 as the spacer layer 106 exhibits
desired properties in the body centered (bcc) (200) texture.
[0037] The magnetoresistance device 100 may include a seed layer
structure 112. The seed layer structure 112 may be arranged such
that the soft magnetic layer 104 is disposed between the seed layer
structure 112 and the first spin-polarizing layer structure 108.
The seed layer structure 112 may include at least one layer. The at
least one layer of the seed layer structure 112 may include a
material or a combination of materials selected from a group of
materials consisting of tantalum, chromium, titanium, nickel,
tungsten, ruthenium, palladium, platinum, zirconium, hafnium,
silver, gold, aluminum, antimony, molybdenum, tellurium, cobalt
iron, cobalt iron boron and cobalt chromium. The at least one layer
of the seed layer structure 112 may have a thickness ranging from
about 0 nm to about 7 nm. In other words, the seed layer structure
112 may have a thickness ranging from about 0 nm to about 7 nm.
[0038] In one embodiment, the at least one layer of the seed layer
structure 112 may be a conductive electrode 114. When the at least
one layer of the seed layer structure 112 is used as the electrode
114, the at least one layer of the seed layer structure 112 may
have a thickness greater than 7 nm.
[0039] The number of layers of the seed layer structure 112 can
vary for different embodiments. In one embodiment, the capping
layer structure 112 may include only one layer 113. The layer 113
may include palladium. The layer 113 may have a thickness of about
50 .ANG..
[0040] In another embodiment (e.g. as illustrated in FIG. 1), the
seed layer structure 112 may include a first layer 113 and a second
layer 115. The first layer 113 may be disposed between the soft
magnetic layer 104 and the second layer 115. The first layer 113
may include palladium. The second layer 115 may include tantalum.
The second layer 115 can be used as an adhesion layer to a
substrate 120. The second layer 115 may have a thickness of about
50 .ANG..
[0041] The seed layer structure 112 may provide a hexagonal close
packing (hcp) (002) texture, a face-centered (fcc) (111) texture or
a body centered (bcc) (200) texture. The seed layer structure 112
may help the soft magnetic layer 104 (e.g. the stacks 202 of the
soft magnetic layer 104) to grow in fcc (111) orientation and thus,
achieving perpendicular magnetic anisotropy (PMA) in the stacks
202. A seed layer structure 112 with a smaller thickness is
desirable for having a more coherent tunneling through the spacer
layer 106. Perpendicular magnetic anisotropy (PMA) may be achieved
in the soft magnetic layer 104 with a minimum thickness of about 30
.ANG. for the seed layer structure 112.
[0042] The magnetoresistance device 100 may further include a
capping layer structure 116. The capping layer structure 116 may be
arranged such that the hard magnetic layer 102 is disposed between
the capping layer structure 116 and the second spin-polarizing
layer structure 110. The capping layer structure 116 may be part of
the electrode 114.
[0043] The capping layer structure 116 may include at least one
layer. The at least one layer of the capping layer structure 116
may include a material or a combination of materials selected from
a group of materials consisting of tantalum, chromium, titanium,
nickel, tungsten, ruthenium, palladium, platinum, zirconium,
hafnium, silver, gold, aluminum, antimony, molybdenum, tellurium
and cobalt chromium. In one embodiment, the capping layer structure
116 may have a thickness ranging between about 30 .ANG. and about
150 .ANG..
[0044] The number of layers of the capping layer structure 116 can
vary for different embodiments. In one embodiment, the capping
layer structure 116 may include only one layer 117. The layer 117
may include palladium. The layer 117 may have a thickness of about
50 .ANG..
[0045] In another embodiment (e.g. as illustrated in FIG. 1), the
capping layer structure 116 may include a first layer 117 and a
second layer 118. The first layer 117 may be disposed between the
hard magnetic layer 102 and the second layer 108. The first layer
117 may include palladium. The second layer 118 may include
tantalum or ruthenium. The second layer 118 can be used to avoid
oxidation. The first layer 117 may have a thickness of about 50
.ANG.. The second layer 118 may have a thickness of about 50
.ANG..
[0046] In one embodiment, the substrate 120 may be disposed
adjacent the seed layer structure 112 (e.g. the second layer 115 of
the seed layer structure 112). In one embodiment, the substrate 120
includes but is not limited to silicon dioxide, silicon, silicon
nitride, magnesium oxide and glass.
[0047] In one embodiment, the magnetoresistance device 100 has the
hard magnetic layer 102 arranged above the spacer layer 106 and the
soft magnetic layer 104 arranged below the spacer layer 106.
[0048] In another embodiment, the magnetoresistance device 100 may
have the hard magnetic layer 102 arranged below the spacer layer
106 and the soft magnetic layer 104 arranged above the spacer layer
106.
[0049] FIG. 3 shows a three-dimensional view of a magnetoresistance
device 300 according to one embodiment. The magnetoresistance
device 300 is similar to the magnetoresistance device 100 except
that the soft magnetic layer 104 includes a further multi-layer
structure 302. The further multi-layer structure 302 has identical
or similar structure and materials as the multi-layer structure
200. At least one of the multi-layer structure 200 and the further
multi-layer structure 302 is made of CoFeB/X, where X is platinum
or palladium. The multi-layer structure 200 and the further
multi-layer structure 302 are coupled antiferromagnetically to each
other. The antiferromagnetic coupling between the multi-layer
structure 200 and the further multi-layer structure 302 are
obtained through the use of thin layers 304. The thin layers 304
may include but are not limited to ruthenium, rhodium, and an alloy
of ruthenium and rhodium.
[0050] The thicknesses of the various layers of the
magnetoresistance device 300 can be adjusted such that the
magnetoresistance device 300 has a desirable magnetoresistance. The
total number of stacks 202 (e.g. total number of the first layer
204 and the second layer 206) in the magnetoresistance device 300
can be higher than the total number of stacks 202 in the
magnetoresistance device 100. Perpendicular magnetic anisotropy
(PMA) can be achieved with improved thermal stability.
[0051] In short, the magnetoresistance device 300 can have a dual
Magnetic Tunneling Junction (MTJ) with two soft magnetic layers
(e.g. 200, 302) made of at least one multilayer of (CoFeB/X) where
X is Pt or Pd. The magnetoresistance device 300 use e.g. CoFeB/Pd
multilayers as the soft magnetic layer to achieve lower switching
current as well as high thermal stability which can allow a
decrease of the design structure size to 40 nm and consequently,
achieving higher storage.
[0052] FIG. 4 shows a schematic diagram of a magnetoresistance
device 400 according to one embodiment. The magnetoresistance
device 400 includes a hard magnetic layer 402 and a soft magnetic
layer 404. The soft magnetic layer 404 has a multi-layer stack
structure 406. The multi-layer stack structure 406 may have at
least one first layer 408 of a first material and at least one
second layer 410 of a second material. For illustration purposes,
the multi-layer stack structure 406 has three first layers 408 of
the first material and three second layers 410 of the second
material. The three first layers 408 of the first material and the
three second layers 410 of the second material are arranged in an
alternating arrangement.
[0053] In one embodiment, the first material may include a cobalt
based magnetic material. The cobalt based magnetic material may
have a formula Co--X--Y. X may include iron, and Y may include
boron or boron nitride.
[0054] The first material may be cobalt-iron-boron nitride
(CoFeBN). CoFeBN is a soft magnetic material which can provide a
low switching current.
[0055] In one embodiment, the second material may include platinum,
palladium or nickel. Nickel is a magnetic material. By using nickel
for the second material, a higher spin-polarization and
magnetoresistance can be achieved.
[0056] The magnetoresistance devices 100, 300, 400 described above
can have a low switching current that can be used in spin-transfer
torque magnetic random access memory (STT-MRAM). In MRAM
applications, the magnetoresistance devices 100, 300, 400 may be
part of a memory circuit, along with transistors that provide the
read and write currents. The magnetoresistance devices 100, 300,
400 can work as or can be part of a multi-level MRAM. The
magnetoresistance devices 100, 300, 400 can also be applicable to
read-sensors of hard disk drives and magnetic field sensors.
[0057] FIG. 5 shows a graph 500 illustrating a hysteresis loop of
the magnetoresistance device 100 for different thicknesses of the
seed layer structure 112. In one embodiment, the seed layer
structure 112 may include palladium. The soft magnetic layer 104
may include a CoFeB/Pd multi-layer structure.
[0058] Plot 502 shows normalized magnetic moment plotted against
perpendicular applied field for a seed layer structure having a
thickness of 0 .ANG. (0 nm). Plot 504 shows normalized magnetic
moment plotted against perpendicular applied field for a seed layer
structure having a thickness of 10 .ANG. (1 nm). Plot 506 shows
normalized magnetic moment plotted against perpendicular applied
field for a seed layer structure having a thickness of 30 .ANG. (3
nm). Plot 508 shows normalized magnetic moment plotted against
perpendicular applied field for a seed layer structure having a
thickness of 50 .ANG. (5 nm). Plot 510 shows normalized magnetic
moment plotted against perpendicular applied field for a seed layer
structure having a thickness of 70 .ANG. (7 nm).
[0059] It can be observed from graph 500 that the hard magnetic
layer 102 and the soft magnetic layer 104 switch at different
fields. Using CoFeB/Pd for the soft magnetic layer 104, can achieve
the switching of the hard magnetic layer 102 and the soft magnetic
layer 104 at different fields. It can also be observed that there
is a larger difference between the switching fields of the hard
magnetic layer 102 and the soft magnetic layer 104 for the seed
layer structure 112 having a thickness of 30 .ANG. (3 nm) and
above. Therefore, a thickness of 30 .ANG. (3 nm) and above is
preferred for the seed layer structure 112 due to the distinct
switching between the hard magnetic layer 102 and the soft magnetic
layer 104.
[0060] FIG. 6 shows a graph 600 illustrating a magnetoresistance
(MR) behavior of the magnetoresistance device 100 for different
thicknesses of the seed layer structure 112. In one embodiment, the
seed layer structure 112 may include palladium. The soft magnetic
layer 104 may include a CoFeB/Pd multi-layer structure. Electric
current flows in the film plane, i.e. current-in-plane (CIP)
configuration.
[0061] Plot 602 shows magnetoresistance plotted against
perpendicular applied field for a seed layer structure having a
thickness of 4 .ANG. (0.4 nm). Plot 604 shows magnetoresistance
plotted against perpendicular applied field for a seed layer
structure having a thickness of 6 .ANG. (0.6 nm). Plot 606 shows
magnetoresistance plotted against perpendicular applied field for a
seed layer structure having a thickness of 8 .ANG. (0.8 nm). Plot
608 shows magnetoresistance plotted against perpendicular applied
field for a seed layer structure having a thickness of 12 .ANG.
(1.2 nm). Plot 610 shows magnetoresistance plotted against
perpendicular applied field for a seed layer structure having a
thickness of 16 .ANG. (1.6 nm).
[0062] The thickness of the seed layer structure 112 can be chosen
to achieve optimized values of perpendicular magnetic anisotropy
and a high magnetoresistance (MR). Too large values of the
thickness of the seed layer structure 112 may result in a reduced
tunneling magnetoresistance (TMR) as the soft magnetic layer 104
(which may be formed with fcc (111) texture) may affect the
formation of the spacer layer 106 (e.g. magnesium oxide (MgO) bcc
(200) tunnel barrier). Consequently, this may result in a lower
magnetoresistance (MR). On the other hand, the seed layer structure
112 having a too thin layer may not be helpful to promote
perpendicular magnetic anisotropy. As shown in FIG. 6, the seed
layer structure 112 having a thickness of about 0.4 nm to about 0.6
nm shows the highest MR value (see plot 602 and plot 604).
[0063] FIG. 7 shows a graph 700 illustrating a magnetoresistance
(MR) behavior of the magnetoresistance device 100. In one
embodiment, the soft magnetic layer 104 may include a CoFeB/Pd
multi-layer structure. The hard magnetic layer 102 may include a
Co/Pd multi-layer structure. The spacer layer 106 may include MgO.
The first spin-polarizing layer structure 108 and the second
spin-polarizing layer structure 110 may include CoFeB. The seed
layer structure 112 may include palladium. Electric current may
flow perpendicular to the film plane, i.e.
current-perpendicular-to-plane (CPP) configuration.
[0064] Plot 702 shows magnetoresistance plotted against
perpendicular applied field for CPP configuration of the
magnetoresistance device 100 (after patterning). Plot 704 shows
magnetoresistance plotted against perpendicular applied field for
CIP configuration of the magnetoresistance device 100 (before
patterning). The inset 706 shows a magnified graph 700 of the plot
702 and the plot 704 from 0 Oe to 1000 Oe of the perpendicular
applied field. It can be observed from graph 700 that the switching
fields of the hard magnetic layer 102 and the soft magnetic layer
104 increase after patterning.
[0065] Switching fields of materials used in conventional devices
also increase after patterning. FIG. 8 shows a plot 802 of
CIP-giant magnetoresistance (GMR) of a conventional single spin
valve (SSV) unpatterned thin film, a plot 804 of CPP-GMR of 100 nm
diameter device pillar and a plot 806 of CPP-GMR of 150 nm diameter
device pillar. It can be observed that the switching field of Co/Pd
multilayer increases from about a few hundred Oe before patterning
to 4-5 kOe after patterning. This indicates that the Co/Pd
multilayer is suitable to be used for a hard magnetic layer.
However, if the Co/Pd multilayer is used for a soft magnetic layer,
its coercivity will increase. As such, a higher switching current
may be required for the Co/Pd multilayer.
[0066] FIG. 9 shows a plot 902 of a switching field of a soft
magnetic layer 104 of the magnetoresistance device 100 plotted
against a size of the magnetoresistance device 100. FIG. 9 also
shows a plot 904 of magnetoresistance of the magnetoresistance
device 100 plotted against the size of the magnetoresistance device
100. In one embodiment, the soft magnetic layer 104 may include a
CoFeB/Pd multi-layer structure. The CoFeB composition of the soft
magnetic layer 104 may be Co.sub.20Fe.sub.60B.sub.20. The CoFeB
layer of the soft magnetic layer 104 may have a thickness of about
3 .ANG.. The Pd layer of the soft magnetic layer 104 may have a
thickness of about 6 .ANG.. The soft magnetic layer 104 may have
three stacks of the CoFeB layer and the Pd layer. The hard magnetic
layer 102 may include a Co/Pd multi-layer structure. The spacer
layer 106 may include MgO. The first spin-polarizing layer
structure 108 and the second spin-polarizing layer structure 110
may include CoFeB. The seed layer structure 112 may include
palladium. The seed layer structure 112 may have a thickness of
about 30 .ANG..
[0067] It can be observed that the switching field of the soft
magnetic layer 104 does not increase significantly when the size of
the magnetoresistance device 100 decreases. It can also be observed
that the magnetoresistance of the magnetoresistance device 100
increases when the size of the magnetoresistance device 100
decreases.
[0068] Therefore, using CoFeB/Pd multi-layer structure for the soft
magnetic layer 104 can allow scaling down of the dimensions of the
magnetoresistance device 100. The reduction in the dimensions of
the magnetoresistance device 100 can achieve higher
magnetoresistance.
[0069] Thus, the magnetoresistance devices described above can
provide a reduced size, a low switching current, a high thermal
stability and a higher storage density.
[0070] While the preferred embodiments of the devices and methods
have been described in reference to the environment in which they
were developed, they are merely illustrative of the principles of
the inventions. Other embodiments and configurations may be devised
without departing from the spirit of the inventions and the scope
of the appended claims.
* * * * *